In signal transmission applications where the average or DC component of a serially transmitted binary signal is non-zero, the DC component of the signal must be restored at the receiver in order to achieve accurate data reproduction. Where the transmission medium is a coaxial cable which includes AC coupling methods for signal transmission, there are two steps required to recover the transmitted data. The first step involves high frequency equalization to compensate for losses during transmission in the cable. The second step involves DC restoration of the equalized signal to recover the low frequency and DC components which are lost through the coupling circuits.
Quantized Feedback (QFB) is the standard technique for DC restoration of an AC coupled binary signal. The Quantized Feedback method has been utilized in practical implementations for cable equalizers for serial digital transmission applications. However, the Quantized Feedback method is sensitive to variations in the amplitude and rise time of the input waveform. As will be appreciated by one skilled in the art, this sensitivity places considerable emphasis on the performance of the high frequency equalizer because as the length of the transmission cable increases, the signal losses become more severe and precise equalization will eventually be impossible. As a result of this sensitivity, the Quantized Feedback method can introduce jitter into the restored waveform.